Five-year-old Emily Hardesty returned from recess sweaty and tired from running around the playground. She and her classmates flopped down on their stomachs as teacher Brenda Queen played some new age instrumental music to ease the children into afternoon lessons.

"Emily, did you go to sleep?" Queen asked as the little girl nodded off. "I need you to listen."

It was four hours into the school day, with 2 1/2 more to go--a long day for an active girl like Emily, who was still adjusting to her new schedule. Last month, kindergarten became an all-day affair for her and 13 other youngsters at Sunderland Elementary in Calvert County, extending the 2 1/2-hour-days that began in August.

For the first time, Calvert County is offering at least one all-day kindergarten class in each of its elementary schools, as are a growing number of school districts throughout the Washington area and the country.

Increasingly, educators say, youngsters arrive at school without the basic skills needed to keep up academically, emotionally and socially. It is not uncommon to find children who think that purple is green, "c" is "k," and a circle is a square.

"If they have trouble with that, you know they'll have trouble all the way," Queen said.

Proponents say the extra individualized attention and constant repetition that an all-day kindergarten program offers can correct that. And research shows that kindergartners who attend a full day of school tend to do better academically in the first grade.

Also welcomed by busy parents seeking alternatives to day care, all-day kindergarten is offered in all Stafford County, Fauquier County and Alexandria schools. D.C. schools for years have offered all-day kindergarten, plus at least one all-day pre-kindergarten class. This year, Arlington County school officials converted half-day kindergarten classes to a full 6 1/2-hour day in each of the county's 21 elementary schools.

"If a school system wants to promote the notion of student readiness, this is a very effective way of doing it, with the caveat that the class size is reasonable," said Rolf Grafwallner, chief of the early learning section for the Maryland Department of Education. "It's definitely catching on."

Early childhood education experts caution that all-day kindergarten programs are effective if they offer solid instruction, and not just play. And the instruction and guidance should continue at home, said Anne Soderman, professor of early childhood education at Michigan State University.

"How well a child is going to be prepared also depends on how much preparation the child gets with parents, how much reading is done, how much conversation goes on with their parents," she said.

While many large school districts offer all-day kindergarten in some schools, few offer the program systemwide, largely because of the extra staff required. In Alexandria, which moved to a complete full-day kindergarten program in 1996, the price tag for providing all-day kindergarten classes in 12 schools this year was $4.3 million.

For school districts already feeling the pinch of rapidly growing student populations, adding all-day kindergarten requires more classrooms. And in the midst of a growing teacher shortage, finding extra kindergarten instructors is no easy task.

"It would just be next to impossible," said Patti Caplan, spokeswoman for Howard County schools, where fewer than 10 of 37 elementary schools offer extended kindergarten to students with academic difficulties. "We would love to do it and as soon as our elementary school population declines, we will."

Montgomery County once offered all-day kindergarten in 37 elementary schools but cut back to nine in 1992 to accommodate increased enrollment systemwide.

New School Superintendent Jerry D. Weast has proposed expanding all-day kindergarten from nine to 28 schools as part of his plan to close the achievement gap between black and Hispanic students and their classmates. Offering at least one full-day kindergarten class at more than 120 elementary schools would cost the school district $10 million, Montgomery school officials said.

"We're seeing that the gap starts quite early," said Pamela Prue, director of early childhood services for Montgomery County schools. "The research clearly shows that for targeted youngsters, high-quality programming during a longer day does generate benefits."

In Calvert, all-day kindergarten at 11 elementary schools--a 12th elementary school offers only grades 3 to 5--will cost $370,000 this year. School officials said they consider the program an important investment to head off the need for remedial work in later school years.

Teachers there spent the first month of school observing and testing students' language development, ability to follow directions and motor skills. They also looked for children who could not say their names without looking at their name tags or who did not recognize colors. With parents' permission, educators assigned students who were at-risk of falling behind to an all-day curriculum.

Each day, the selected children spend the morning in regular kindergarten classes. Once their classmates' 2 1/2-hour day ends, the all-day students gather in one classroom for the second portion of the day. There, the teacher reinforces the lessons of the morning: Children go through the alphabet once again, read more stories, write and draw.

On a recent day, Queen played a game with six of her students who sat in a circle around her. Each student had three picture cards, each showing one part of a three-sequence event. Queen asked students to place the pictures in the order that they occurred, then watched.

"Megan, are you sure you want this card as your first card?" she asked one student, who was looking at three cards showing a dog jumping up to snag a treat from a boy's hand.

The girl sat silently, holding a card that showed the dog leaping, in mid-air.

"Talk to me," Queen encouraged her forcefully. Indeed, "talk to me" is the phrase Queen uses often in the classroom to get students talking in complete sentences.

Queen has noticed improvements in her students' language skills and ability to follow directions. When school first started, some students asked to cut in a straight line often produced shreds of paper. Others could not say their names without cues from their teacher.

That was not the case with Emily Hardesty, her parents said. When she started kindergarten, Emily was just 4 and had never been around so many other children and under the direction of anyone other than her parents.

Emily fell behind because she did not take school seriously, her father, Tim Hardesty, said, failing to follow directions and refusing to answer questions properly--even when she knew the answers. When school officials broached the idea of all-day kindergarten with Emily's parents, they welcomed the idea.

"She was in there for two hours. That isn't enough time to do anything with a kid," Hardesty said. "It was all pretend to her."

Now, Emily's father said, she is making progress. She knows her ABC's and memorizes nursery rhymes with ease.

"Emily is smart, but they wanted her to catch up," he said. "This is the time to make them catch up, when they're this little, not when they're in ninth grade."

CAPTION: At Sunderland Elementary School, teacher Brenda Queen leads her kindergartners in an afternoon stretch. Last month, kindergarten became an all-day affair at Sunderland.

CAPTION: At Sunderland Elementary, Joe Sims III plays alphabet bingo. School officials said they consider the all-day kindergarten program to be an important investment.

CAPTION: At Mount Harmony Elementary School in Calvert County, Naaila Cooke, left, and Alyssa Murias read to each other in a homemade tepee.

CAPTION: Emily Kong makes her way down the jungle gym during recess at Sunderland Elementary School.